Vitamin B12 Deficiency in Black Adults: A Missed Cause

Vitamin B12 deficiency gets confused with iron-deficiency anemia, and that confusion is dangerous. Both cause fatigue. But low B12 produces a different kind of anemia, one with large red blood cells instead of small ones, and it does something iron deficiency does not: it damages nerves and the spinal cord. The NIH Office of Dietary Supplements states it plainly: "These neurological symptoms can occur without anemia, so early diagnosis and intervention is important to avoid irreversible damage." The window to fix nerve damage closes. Caught early, B12 deficiency is fully treatable. Caught late, the numbness, balance problems, and memory changes can stay.

Vitamin B12 (cobalamin) builds healthy red blood cells, keeps your nervous system working, and helps make DNA. Your body cannot make it. You get it from animal foods (meat, fish, eggs, dairy) or supplements. When B12 drops, two systems fail. Red blood cell production goes wrong, producing megaloblastic anemia, which the NIH describes as anemia "characterized by large, abnormally nucleated red blood cells." And the protective coating on nerves breaks down, which is what causes the numbness, the unsteady walking, and the cognitive symptoms.

This is the split that matters. Iron-deficiency anemia makes red cells small (microcytic). B12 deficiency makes them large (macrocytic). A clinician reading a complete blood count sees the difference in a value called MCV. Both leave you tired, but only B12 deficiency attacks the nervous system. Treating one as if it were the other wastes time the nerves do not have.

Early on, B12 deficiency feels like ordinary exhaustion, which is why it hides. The NIH and MedlinePlus list these signs:

• Fatigue, weakness, palpitations, and pale skin from the anemia.
• A sore, smooth, red tongue (glossitis), and sometimes a burning mouth.
• Numbness and tingling in the hands and feet (paresthesias), often the first nerve sign.
• Trouble with balance and walking as the spinal cord is affected.
• Memory loss, confusion, depression, and irritability. The NIH notes studies linking low B12 to depression, and MedlinePlus lists confusion and dementia-like changes.

The most under-appreciated point in all of this: the nerve and brain symptoms can come first, before the blood count ever looks abnormal. A person can have a normal hemoglobin, even a normal-looking B12 level, and still have B12-driven nerve damage building quietly. Doctors call the advanced form subacute combined degeneration of the spinal cord. If you have unexplained numbness, tingling, or balance problems and a clinician has not checked your B12, that is a gap worth closing. We cover the overlap with diabetes in our piece on numbness and tingling in the hands and feet.

Here is the Black-health angle, and it is backed by data. Black adults carry a higher diabetes burden. CDC's National Diabetes Statistics Report puts diagnosed diabetes at 12.1 percent in non-Hispanic Black adults versus 6.9 percent in non-Hispanic White adults. The HHS Office of Minority Health reports Black adults are about 24 percent more likely than the overall U.S. population to have diabetes. Metformin is the first-line drug for type 2 diabetes, so more Black adults are on it, for longer.

Metformin lowers B12. The NIH states it "might reduce the absorption of vitamin B12 and significantly reduce serum vitamin B12 concentrations." The effect grows over time. In the Diabetes Prevention Program Outcomes Study, a large randomized trial, low B12 was more common in the metformin group than placebo (4.3 percent versus 2.3 percent at year 5; 7.4 percent versus 5.4 percent by year 13). The authors concluded that "routine measurement of vitamin B12 for metformin-treated individuals should be considered."

The American Diabetes Association now reflects this in its Standards of Care: periodic B12 testing should be considered in people on long-term metformin, especially at doses of 1,500 mg a day or more, after 4 to 5 years of use, or when there is anemia or peripheral neuropathy. If you have been on metformin for years and nobody has checked your B12, ask. It is a cheap blood test. For more on living with the drug, see metformin side effects in Black patients.

Metformin is not the only culprit. B12 needs stomach acid and a protein called intrinsic factor to be absorbed, so anything that interferes with either one can cause deficiency.

• Acid-reducing medicines. Long-term proton pump inhibitors (omeprazole, pantoprazole) and H2 blockers cut stomach acid, which the body needs to free B12 from food. A 2013 JAMA study of more than 25,000 people found that two or more years of PPI use was associated with B12 deficiency.
• Pernicious anemia. An autoimmune disease in which the body attacks the stomach cells that make intrinsic factor. Without it, B12 cannot be absorbed no matter how much you eat. It is the classic cause and needs lifelong treatment.
• Older age. The stomach makes less acid with age, so absorption drops. Many older adults are low even with a decent diet.
• Plant-based diets. B12 is almost entirely in animal foods. Strict vegetarians and vegans need a supplement or fortified foods, or they will run low over time.
• Stomach or bowel surgery (including weight-loss surgery) that removes the parts where B12 is absorbed.

Diagnosis starts with a serum B12 blood test, often alongside a complete blood count that may show large red cells. The catch is that the B12 level is unreliable in the gray zone. A result that lands borderline (roughly 200 to 300 pg/mL) does not rule deficiency in or out, and some people have real nerve symptoms with a level that looks normal.

That is what two confirmatory tests are for: methylmalonic acid (MMA) and homocysteine. Both rise when B12 is truly low at the cellular level, often before the serum B12 reads low. An elevated MMA is the more specific of the two. If your B12 is borderline, or if it is normal but you have unexplained numbness, tingling, balance trouble, or memory changes, ask whether an MMA test is warranted. It can catch a deficiency the standard level misses.

B12 deficiency is treatable, and treatment is straightforward. There are two parts: replace the B12, and address why it dropped.

• High-dose oral B12 works for many people, including some with absorption problems, because a small fraction of a large oral dose gets absorbed without intrinsic factor. The NIH notes that high oral doses can normalize B12 about as well as intramuscular shots.
• B12 injections are used when absorption is severely impaired, in pernicious anemia, or when symptoms are serious and you want levels up fast. They are typically frequent at first, then spaced out.
• Treat the cause. If metformin or a PPI is the driver, that does not always mean stopping the drug. It usually means supplementing B12 and monitoring. If it is pernicious anemia, treatment is lifelong. Diet-related deficiency responds to supplements or fortified foods.

The anemia and the early nerve symptoms usually improve with treatment. Long-standing nerve damage may only partly recover, which is the whole argument for catching it early.

If you take metformin or a PPI long-term, are over 60, eat little or no animal food, or have unexplained fatigue or nerve symptoms, ask your clinician for a B12 level at your next visit. It is one tube of blood. Bring up your medications and your diet so the test is interpreted in context, and ask about MMA if the result is borderline. A provider who knows the diabetes and metformin picture in Black patients will not dismiss a borderline number. You can find a Black primary care clinician in our directory.